knees swollen

dear mr/mrs my aunt’s left knee after 3 days of pain has been swollen(it has been bigger than usuall)(without any impact or hitting to something in a way that she couldnt fold it.her doctor sent out the body fluid. now theres no pain while she just walk a very short distance.what do u think it would be.her test of body fluid was sugar 23protein 5500wbc 8250and her blood test wbc 11.2crp (++) posnow she is about 37 please tell me what her illness is and what is theillness????????? yours sincerly hamzeh mousavi